Merge branch '3.4' into 4.0

* 3.4: (22 commits)
  [DI] Add tests for EnvVarProcessor
  [Bridge\PhpUnit] Fix #26430 Cannot autoload listeners
  Make sure we always render errors. Eventhough labels are disabled
  Make sure form errors is valid HTML
  [HttpKernel] Allow generators in registerBundle
  [TwigBundle] document TwigRenderer BC break in UPGRADE-3.4
  Extra line to bootstrap 3 horizontal layout
  [Serializer] Remove const override
  Update Client.php
  [PhpUnitBridge] Ability to use different composer.json file
  [DomCrawler] FormField: remove an useless return statement
  [Config] ReflectionClassResource check abstract ServiceSubscriberInterface and EventSubscriberInterface
  Display the Welcome Page when there is no homepage defined
  fix regression when extending the Container class without a constructor
  fix the updating of timestamp in the MemcachedSessionHandler
  [SecurityBundle] Make extra character non mandatory in regex
  [Config] Add characters to the regex
  bumped Symfony version to 3.4.7
  updated VERSION for 3.4.6
  updated CHANGELOG for 3.4.6
  ...

Author: nicolas-grekas

Resources/views/Form/bootstrap_3_horizontal_layout.html.twig

@@ -62,4 +62,4 @@ col-sm-10
             {{- form_errors(form) -}}
         </div>{#--#}
     </div>
-{%- endblock checkbox_row %}
+{%- endblock checkbox_row %}

Resources/views/Form/bootstrap_4_layout.html.twig

@@ -203,7 +203,13 @@
                 {% set label = name|humanize %}
             {%- endif -%}
         {%- endif -%}
-        <{{ element|default('label') }}{% if label_attr %}{% with { attr: label_attr } %}{{ block('attributes') }}{% endwith %}{% endif %}>{{ translation_domain is same as(false) ? label : label|trans({}, translation_domain) }}{{- form_errors(form) -}}</{{ element|default('label') }}>
+        <{{ element|default('label') }}{% if label_attr %}{% with { attr: label_attr } %}{{ block('attributes') }}{% endwith %}{% endif %}>{{ translation_domain is same as(false) ? label : label|trans({}, translation_domain) }}{% block form_label_errors %}{{- form_errors(form) -}}{% endblock form_label_errors %}</{{ element|default('label') }}>
+    {%- else -%}
+        {%- if errors|length > 0 -%}
+        <div id="{{ id }}_errors" class="mb-2">
+            {{- form_errors(form) -}}
+        </div>
+        {%- endif -%}
     {%- endif -%}
 {%- endblock form_label %}
 
@@ -261,12 +267,12 @@
 
 {% block form_errors -%}
     {%- if errors|length > 0 -%}
-        <div class="{% if form is not rootform %}invalid-feedback d-block{% else %}alert alert-danger{% endif %}">
-            <ul class="list-unstyled mb-0">
-                {%- for error in errors -%}
-                    <li><span class="initialism form-error-icon badge badge-danger">{{ 'Error'|trans({}, 'validators') }}</span> <span class="form-error-message">{{ error.message }}</span></li>
-                {%- endfor -%}
-            </ul>
-        </div>
+        <span class="{% if form is not rootform %}invalid-feedback d-block{% else %}alert alert-danger{% endif %}">
+            {%- for error in errors -%}
+                <span class="mb-0 d-block">
+                    <span class="initialism form-error-icon badge badge-danger">{{ 'Error'|trans({}, 'validators') }}</span> <span class="form-error-message">{{ error.message }}</span>
+                </span>
+            {%- endfor -%}
+        </span>
     {%- endif %}
 {%- endblock form_errors %}